Solenoid switch circuit verification - Electronic Circuits Projects Diagrams Free

richacm · 12th June 2008, 10:00 PM

Hi can someone verify my little circuit please.

When I switch on I need 0.1A to go one way through a solenoid and when I switch off I need the 0.1A to go the other way.

Much appreciated.

Craig

blueroomelectronics · 12th June 2008, 10:06 PM

Can you use a center off double pole switch? Really easy to reverse current with one.

Your circuit has floating bases, you may want to add a couple more resistors to keep the tied to power & gnd.

richacm · 12th June 2008, 10:10 PM

Yeah I can use what ever I like....I just thought transistors would work ok.

Instead of having a manual switch I am going to send 5V directly to the Base of the transistors from a PIC chip. I.e. to turn ON I send 5V to the Base of the ON transistors and OFF sends 5V to the Base of the OFF transistors.

Thanks.

Craig

richacm · 12th June 2008, 10:11 PM

Quote:

Originally Posted by blueroomelectronics

Can you use a center off double pole switch? Really easy to reverse current with one.

Your circuit has floating bases, you may want to add a couple more resistors to keep the tied to power & gnd.

Cool, will have a look

mneary · 12th June 2008, 10:14 PM

You need two PNP and two NPN transistors.

richacm · 12th June 2008, 10:22 PM

Quote:

Originally Posted by mneary

You need two PNP and two NPN transistors.

Thanks for that...missed the PNP, NPN relations.

Attached is new circuit. I still have floating bases though as pointed out by blueroom....how do I stop that?

Cheers,

Craig

mneary · 12th June 2008, 10:26 PM

Sorry I didn't notice before... you also need to swap the PNP emitters with one another.

Your bases won't be floating when you hook them to the PIC.

richacm · 12th June 2008, 10:33 PM

Quote:

Originally Posted by mneary

Sorry I didn't notice before... you also need to swap the PNP emitters with one another.

Sorry I don't follow that one. The PNP Emitters go to either solenoid terminal to make the current go from 0.1A one way or 0.1A the other way....that's correct isn't it? Oh that little symbol in front of the 0.1A is a ~ for approximate. It looks like a "-" negative when its small.

Quote:

Your bases won't be floating when you hook them to the PIC.

Ah ok.

mneary · 12th June 2008, 10:42 PM

Can you put numbers on the transistors? Would be easier to explain.

richacm · 12th June 2008, 10:47 PM

Numbers attached.

Thanks

richacm · 13th June 2008, 02:45 AM

I think I know what you mean....I needed NPN transistors didn't I?

As in the diagram.

mneary · 13th June 2008, 06:17 PM

Transistors 2 and 4 should be PNP. Emitters 1 and 2 should be connected together. Emitters 3 and 4 together too.

Sorry I took so long to reply, my internet at home is down.

richacm · 13th June 2008, 08:24 PM

But if 1 and 2 emitters were connected together then the current would go straight to ground wouldn't it? I wouldn't get any current going through the solenoid.

Sorry I am not following what you mean.

mneary · 13th June 2008, 08:37 PM

Here's what I mean: The two inputs are MCU ports. Won't work with a switch without additional resistors. Probably should replace the 1Ks with 220 or 270 ohms.

richacm · 13th June 2008, 08:52 PM

Quote:

Originally Posted by mneary

Here's what I mean: The two inputs are MCU ports. Won't work with a switch without additional resistors. Probably should replace the 1Ks with 220 or 270 ohms.

Thanks, but when the Off/On switch is on wouldn't there be a straight path down to ground missing the solenoid?

EDIT: I think I am not clear on what a PNP transistor does. Is it the opposite of an NPN? In that it is on when the Base is Low and Off when the base is High?

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12th June 2008, 10:06 PM	(permalink)
blueroomelectronics	Can you use a center off double pole switch? Really easy to reverse current with one. Your circuit has floating bases, you may want to add a couple more resistors to keep the tied to power & gnd. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com Last edited by blueroomelectronics; 12th June 2008 at 10:07 PM.

12th June 2008, 10:10 PM	(permalink)
richacm	Yeah I can use what ever I like....I just thought transistors would work ok. Instead of having a manual switch I am going to send 5V directly to the Base of the transistors from a PIC chip. I.e. to turn ON I send 5V to the Base of the ON transistors and OFF sends 5V to the Base of the OFF transistors. Thanks. Craig Last edited by richacm; 12th June 2008 at 10:11 PM.

12th June 2008, 10:14 PM	(permalink)
mneary	You need two PNP and two NPN transistors.

12th June 2008, 10:26 PM	(permalink)
mneary	Sorry I didn't notice before... you also need to swap the PNP emitters with one another. Your bases won't be floating when you hook them to the PIC.

12th June 2008, 10:42 PM	(permalink)
mneary	Can you put numbers on the transistors? Would be easier to explain.

13th June 2008, 06:17 PM	(permalink)
mneary	Transistors 2 and 4 should be PNP. Emitters 1 and 2 should be connected together. Emitters 3 and 4 together too. Sorry I took so long to reply, my internet at home is down. Last edited by mneary; 13th June 2008 at 06:19 PM.

13th June 2008, 08:24 PM	(permalink)
richacm	But if 1 and 2 emitters were connected together then the current would go straight to ground wouldn't it? I wouldn't get any current going through the solenoid. Sorry I am not following what you mean. Last edited by richacm; 13th June 2008 at 08:25 PM.